Tillage is one of the important management tools, and it may affect soil structure. In this research, the effect of 3 tillage systems including conventional (CT), minimum (MT) and no tillage (NT) together with crop residues of 0, 30 and 60 percentage on stability of soil structure was studied. This research was performed as a randomized complete blocks design in three replications at Khorasan Razavi province (Iran) for a rotation of 4 years (wheat, canola, wheat, tomato). The whole soil stability (WSSI), and normalized stability indices (NSI) were determined. The results showed that indicators of soil structure were influenced by management practices (plant residues and tillage), and they were significantly decreased by increasing tillage intensity, while NT and MT improved soil structure stability indicators significantly compared to the CT due to increasing the soil organic matter. The mean of WSSI in NT was 9 and 64% more than the MT and CT systems, respectively. Also, the average of NSI in NT was 9 and 95% greater than the MT and CT systems, respectively. Also, among different aggregate size classes, 2-9.5 mm aggregate size had the highest WSSI values in all treatments. In general, the values of WSSI and NSI were NT > MT > CT. In addition, among studied treatments in terms of soil structure stability, NT with 60% of residues was the best treatment and CT with no residues was the worst one. Therefore, the conservation tillage is recommended to increase stability of soil structure and to prevent land degradation.

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